docs: add high-risk tool gating recipe

[maxpetrusenkoagent]

Summary

• add a Core cookbook recipe for gating high-risk tool calls
• show a DeFi token safety example where the action tool enforces the safety check instead of relying on model instructions alone
• link the new recipe from the cookbook index

Verification

• uv run python check_md_code_blocks.py docs/src/user-guide/core-user-guide/cookbook/gating-high-risk-tool-calls.md
• Extracted the recipe's Python code block and ran main() with uv run python; output: example main passed
• uv run sphinx-build -b html -W --keep-going docs/src docs/build reached the new page and failed only on existing optional dependency autodoc warnings (cv2, chromadb, redisvl, llama_cpp, ollama, semantic_kernel, graphrag, json_schema_to_pydantic).

Closes #7531